Air flow choke for bowl mills



w. R. WOOD 2 9 AIR FLOW CHOKE FQR BOWL MILLS Filed Dec. 22, 1938 2 Sheets-Sheet l INVENTOR ATTORNEY.

" July 2, 1940.

w. R. woon l ,2

AIR FLOW CHOKE FGR BOWL MILLS Filed Dec. 22, 1958 2 Sheets-Sheet 2 INVENTOR My? ZZ %0a MEX ATTORNEY Patented July 2, 1940 UNITED STATES AIR FLow: CHOKE FOR BOWL MILLS Wilfred R. Wood, New York, N. Y., assignor to Combustion Engineering Company, Inc., New. York, N. Y., a corporation of Delaware Application December 22,. 1938, Serial No. 247,162

10 Claims.

This invention relates to certain new and useful improvements in arotary bowl mill adapted to grind andflpulverize solid materials, for example, coal or rock, and more particularly to means for 5 controlling the air flow through a mill of this type.

Briefly described, the mill is of the type including an upwardly opening bowl or grinding ring which is rotatable about a central vertical axis within a substantially closed housing or casing. A plurality of grinding elements, for example, rollers each freely rotatable about its own axis, are suspended within the bowl or ring so as to be forcedunder pressure toward the upwardly and outwardly projecting inner side wall of the.

bowl, or against the material carried thereby, the rollers being rotated by contact with this material. The side walls of the bowler ring are spaced from the side walls of the housing so as to provide an annular air passage around the bowl, air being admitted to the lower portion of the pass'age and drawn or forced under pressure through the annular passage and thence over the bowl and through outlets in the upper wall of the casing to a separator. sufficiently pulverized material is carried in suspension in the air stream from the easing into and through the separator. The material to be pulverized is introduced from: above into the central portion of the bowl or interior of the ring, and insufficiently pulverized material is returned from the separator for additional grinding treatment. Deflectors are positioned in the casing at the outer side of and above the annular air passage to return some insufficiently i into the bowl for further treatment. The heaviest waste materials, for example, tramp iron, fall through the annular passage into the lower portion of the casing and are discharged through a passage in the bottom of the casing. A mill of the general type described hereinabove is disclosed and claimed in the patent of Joe Crites, No. 2,079,155, granted May 4, 1937.

In a mill of this type, the upward air flow through the annular passage around the bowl must have at least a certain minimum velocity in order to sustain and carry upwardly the pulverized materials spilled or thrown upwardly and With the full width. of the air, passage left unrestricted, the flow of outwardly from the bowl.

i c s air necessary inorder to maintain this minimum velocity would in some cases be excessive. .For

pulverized material thrown from the bowl back will be too much primary air for combustion when the mill is operating under a light load. If the air stream is cut down so as not to provide too much combustion air, there will be insufficient velocity around the bowl to sustain the pulverized coal 5 in the air stream, and the coal will spill over the edge of the bowl and downwardly through the air passage and be discarded along with heavy waste material. of course, the width of the annular passage can be restricted, thus increasing the velocity for a given volume of air, but this restricted passage will then be'too narrow to allow pieces of tramp iron or other foreign materials to pass downwardly between the bowl and housing.

According to the present invention an annular choking means is provided fornormally restricting the effective width and area of the annular air passage, said means being yieldable or outwardly extensible so as to increase the width of the passage when necessary so that tramp iron or other heavy material can fall downwardly through the passage into the lower portion of the casing. This choking means permits the required air velocity to be obtained with a greatly decreased volume of 2 air flow. Specifically, the choking means comprises a circular series of circumferentially aligned sections, eachsection being movably and adjustably positioned in the air passage so as to determine the effective width of the open air pas-.- sage between the section and the rotating bowl. The section-supporting means comprises a spring which will yield to permit the section to be forced outwardly, thus temporarily increasing the width of the passage between the section and bowl.

The principal object of thisinvention is to provide an improved bowl-milllof the type briefly described hereinabove and disclosed more in detail in the specification which follows.

Another object is to provide improved choke means for adjustably and yieldably restricting 0 the effective area of the air passage.

Another object is to provide improved means for controlling the upward flow of air around the bowl of a bowl-mill.

Other objects and advantages of this invention will be more apparent from the following detailed description ofone approved form of apparatus constructed and operating according to the principles of this invention.

In the accompanying drawings:

Fig. l is. a partial elevation and partial vertical section through the mill and separator assembly.

Fig. 2 is a partial horizontal section, taken substantially'on the line 2.2 of Fig.3, showing the lower portion of the mill assembly with the grinding rollers removed.

Fig. 3 is a partial vertical section taken substantially on the line 33 of Fig. 2.

Fig. 4 is a detail horizontal section taken substantially on the line 4-4 of Fig. 3.

This assembly comprises a casing or housing A, the rotatable bowl or container B which is driven and supported by the mechanism indicated generally at C, the grinding rollers D, and

the mechanism indicated generally at E for supporting and exerting adjusted pressure on the rollers. The means shown at F feeds material to be ground into the mill, and the conduit system, indicated generally at G, delivers air under pressure into the lower portion of the mill housing. At H is indicated the mechanism for discharging waste materials from the mill, while at K is shown the separator through which the sufliciently pulverized material is carried out in suspension and from which insufiiciently pulverized material is delivered back into the bowl B. At L is indicated generally the improved choke means for controlling the air-flow through the mill, the addition of this means to the mill combination forming the particular subject matter of the present invention.

The enclosing casing or housing A comprises the base plate I which rests upon the concrete pedestals or foundation 2, the annular side wall 3, and the closure or cover plate 4. The base plate I comprises a central bearing portion 5 in which the hub 6 of bowl B is journaled. The cover plate 4 is provided with a plurality of openings I through which portions of the roller supports E extend, outlet openings 8 which communicate with passages 9 leading intothe separator K, and a central opening H! which communicates with the lower discharge end of separator K for returning material to the mill. The feeding mechanism F also comprises a spout which extends downwardly and inwardly through an opening in cover plate 4 so as to discharge into the bowl D. The top of the mill housing is closed by wall 4 except for the openings hereinabove noted.

The bowl B comprises a central table portion H and an annular side wall comprising a lower portion I2 which flares outwardly at a small angle to the horizontal, and an upper portion 13 which extends upwardly and outwardly at a small angle to the vertical. Preferably a separate grinding track or ring I 4 is mounted on the inner surface of the inclined side wall or ring l3 of the bowl, ring l4 providing the grinding surface opposed to the grinding rollers D.

The driving assembly C comprises a central vertical drive shaft I5 which is keyed within the hub 6 of the bowl B. The upper and lower members l6 and l'l'of a gear casing are secured together and suspended from thebearing portion 5 of base plate I so as to enclose and lubricate the ward thrust on the grinding ring l4. Each roller is freely rotatable on a non-rotary supporting shaft 20 which forms a portion of the supporting assembly E. The grinding roller D is rotatable by contact with the grinding ring I4, or more properly by contact with the material to be ground which is interposed between the tread of the roller and the grinding ring, as will be hereinafter apparent. Each roller-supporting mechanism E comprises a main lever 2! mounted on shaft 22 pivoted in the supporting brackets 23. The adjustable spring mechanism 24 tends to swing the roller assembly in a clockwise direction about the axis 22, as seen at the left of Fig. 1, or in a counter-clockwise direction, as seen at theright of Fig. 1, so as to force the rollers D yieldably against the grindingring I4. As material to be ground finds its way between rollers D and the grinding ring, the springs 24 will yield to permit the rollers to move inwardly, but a predetermined outward pressure will be exerted on the material, this pressure being determined by proper adjustment of the spring mechanisms. The grinding rollers D and supporting mechanisms. E are disclosed in more detail in the Crites Patent 2,079,155 hereinabove referred to.

The material to be ground and pulverized is fed into the housing through chute F, it being understood that this feeding mechanism will also usually include a hopper and rotary feeding mechanism so as to graduate the rate at which material is fed into the mill. This feeding mechanism (not here shown in detail) will also prevent the flow of air through chute F.

Air from any suitable source is delivered through conduit G tangentially into the lower portion of the mill housing through inlet opening 25, thus causing a whirling movement of the air within the housing. This air is delivered into the housing under pressure, but this pressure may be created by a suction at the outlet 26 of separator K. This air stream passes upwardly through the annular channel or passage 21 between the rotating bowl B and the side wall 3 of the casing, thence inwardly over the bowl and out through the passages 9 leading into the upper portion of separator K.

This separator K may be of any suitable type, but is here. shown in the form disclosed in said Crites Patent No. 2,079,155. Briefly described, the air stream carrying pulverized material in suspension passes upwardly through conduits 9 into the annular manifold 28 from which it is discharged tangentially with a whirling motion through outlets 29 into the upper portion of separating chamber 30. The larger and heavier particles of material will separate out and be returned through the central bottom opening l0 into the bowl B for further grinding. The sufficiently pulverized material will remain in suspension and be carried upwardly through outlet conduit 26. This material may then be collected from the air stream by means of a suitable separator, or in the case of pulverized coal, it may be carried directly into a furnace in suspension in the air stream.

Returning now to the description of the grinding process, the material in bowl B will move by centrifugal force toward the outer wall l3 of the bowl and will be ground and pulverized between the rollers D and grinding ring 14. Due to the edge of the bowl.

A plurality of normally stationary deflectors 3| are positioned at spaced intervals circumferentiallyof the housing in the upper and outer por-, .tion thereof adjacent the side wall 3 and top wall 4.

These deflectors are at the outer side of and above the annular air passage 21 and are in the form of substantially verticalvanes which extend diagonally inward from the outer wallof the casing in the direction of rotation of the bowl. (see Fig. 2). An annular rotary deflector 32 is mounted on the upper edge portion of the side wall 13 of the bowl.

, provided with an inner surface sloping upwardly and outwardly toward the stationary deflectors 3i, or may be in the form of an annular angle plate, such as here shown. Material from the bowl will flll in this angle so as to provide an upwardly and outwardly sloping surface, and material which would otherwise be thrown substan-- tially horizontally by centrifugal force will be directed upwardly and outwardly by this sloping surface toward the stationary deflector vanes through the air stream which is moving spirally ing with the discharge Crites Patent No.

upward through annular passage 21, and this air stream will be of suffiicientvolume and velocity to carry sufliciently pulverized material in suspension and eventually carry this material upwardly into separator K, as already described.- Larger particles of material which have not been sufficiently pulverized or reduced in size and which are too heavy to be carried in suspension in-the air stream, will be thrown back through the air stream by the deflecting vanes 3! into the central portion of bowl Band thus return to the grinding cycle. The heavier andlarger pieces of waste material which cannot be ground in the mill and are to be rejected, for example tramp iron, will be thrown outwardly from the; bowl in a more horizontal direction and will fall back through passage 2'! into the lower chamber 33 beneath the bowl.

, ,'I'he discharge mechanism H comprises a discharge opening 34 extending down from chainber33 through the base plate I and communicatchute 35 provided with one-way valve 36 which minimizes the inflow of air through this chute. A plurality of scrapers 31 are carried by. the rotating bowl B these scrapers moving material deposited in chamber 33 around into position to be discharged through opening. Lighter material scraped up by these scrapers will be carried up by the whirling air stream through passage 21 and thence returned into the mill.

. The combination as thus far described is substantially of the form disclosed and claimed in 2,079,155, hereinabove referred to. The air stream forced or drawn upwardly through the mill must comprise a sufficient volsuspension and at the same time this air stream must have suflicient velocity to carry the material upwardly toward the deflectors 3i, and pre- 70 vent any substantial amount of pulverized ma-- terial from falling downwardly through the annular air passage 21. At the same time it is undesirable to utilize too great a volume of air as,

forexample, when pulverized coal is carried directly to a furnace in suspension in this 'air This deflector may be,

stream. When there is only a slight load in the mill the volume of this air stream may be excessive for combustion purposes. It will be apparent that the volume of air can be cut down while maintaining the required velocity by simply narrowing the' annular air passage 21, or restricting its upper outlet. However, the passage will then be of insufficient width to permit large pieces of waste material, such as tramp iron, from filling downwardly into the discharge chamber According to the present invention this problem is solved by the use of the annular air-choke or flow-control means indicated generally at L.

This annularair-choke L normally restricts the to end, so as to form a substantially continuous ring. The upper. edge of each section extends into substantial engagementwith the cover plate i while the lower portion of the section projects inwardly and downwardly so as to overlap the upper outer portion of :bowl B (or the stationary deflector 38 carried by the bowl), the narrow or restricted portion 38 of the air passage being formed between section 39 and the rotating bowl.

Each section 39 is pivotally mounted adjacent its upper end on a pivot pin Ml supported between brackets 4! carried by bolts 42 extending through wall It of the casing. A small housing or socket member 43 secured by bolts M to the lower outer side of section 39 loosely encloses the enlarged head portion #35 of the adjusting bolt 46 which extends out slidably through an opening 41 in the adjacent casing wall 3 (see Fig. 4) The outer portion of bolt orhstem it also extends loosely through. an opening 48 in a yoke member 49 mounted by means of screw bolts 50 on theouter surface of wall 3. is threaded at and is engaged by the adjusting nut or liandwheel 52. A compression spring 53 is confined between the outer wall of yoke 49 and a plate or washer 54 held in a position intermediate the length of stem 46 by pin 55.

It will be apparent that spring 53 tends to force stem M5 and consequently the lower portion of section 39 inwardly, the extent of this inward movement being determined by the adjustment of nut or hand-wheel 52. By adjusting nut 52 the effective width or areaof the upper portion of the air passage is determined. It will also be apparent that whatever the adjustment of the section may be, the lower portion of thesection can always be swung outwardly against the resistance oispringiit so as. to temporarily increase location. Each of the individual choke sections .ume of air to carry the pulverizedmaterial in i large and unpulverized pieces of material from finding their way downwardly through passages 38 and Z'l into the lower discharge chamber 33. It will now be apparent that thenormal effec- The outer portion of stem 46 tivewidth of the air passage can be varied as desired by adjustment of nuts 52 in order to secure the desired volume and velocity of air flow through the mill. Also any or all of the sections of the choke ring are outwardly yieldable at any time to permit material to pass downwardly through the air, passage.

The normally stationary. deflectors 3|, hereinabove described, are conveniently mounted on theinner upper portions of certain of the choke sections 39, forexample, on alternate sections, as indicated in Figs. 2 and 3.

I claim:

.1. A mill comprising a closed casing, a grinding member mountedwithin the casing for rotation about a central vertical axis, said member comprising an upwardly and outwardly inclined grinding ring, a plurality of grinding elements mounted to engage the grinding ring internally, means for introducing material to be ground between the ring and grinding elements, there being an annular air passage between the grinding ring and the enclosing wall of the casing, means for forcing air through this passage to carry away pulverized material in suspension, and a substantially annular choke means mounted in the passage for restricting the effective width of the air passage, said choke means being yieldable to permit the effective width of the passage to be temporarily increased at any location throughout the circumference.

2. A mill comprising a closed casing, a grinding member mounted within the casing for rotation about a central vertical axis, said member comprising an upwardly and outwardly inclined grinding ring, a plurality of grinding elements mounted to engage the grinding ring internally, means for introducing material to be ground between the ring and grinding elements, there being an annular upwardly extending air passage between the grinding ring and the enclosing wall of the casing, means for forcing air through this passage to carry away pulverized material in suspension, a substantially annular choke 'means mounted in the passage for restricting the effective width of the air passage, and means for adjusting the diameter of said choke and hence the effective width of the air passage, said choke being yieldable to permit the effective width of the passage to be temporarily increased at any location throughout the circumference.

3. A mill comprising a closed casing, a grinding member mounted within the casing for rotation about a central vertical axis, said member comprising an upwardly and outwardly inclined grinding ring, a plurality of grinding elements mounted to engage the grinding ring internally, means for introducing material to be ground between the ring and grinding elements, there being an annular air passage between the grinding ring and the enclosing wall of the casing, means .for forcing air through this passage to carry passage for restricting the effective width of the air passage, said choke means comprising a plurality of independently movable sections substantially abutting end to end, each section being pivotally supported adjacent its upper edge on the casing wall, and means for adjustably holding the lower portion of the section toward the outer surface of the ring to select the effective width of the air passage, said means comprising a spring against which the section may be pushed out to temporarily increase the width of the air passage. 1

5. A mill comprising a closed casing, a bowl centrally mounted within the casing for rotation about a vertical axis, means forrotating the bowl, means for introducing material to be ground into the bowl, a plurality of spaced apart rollers mounted to engage inside the upwardly and outwardly extending wall of the bowl and grind the material between the bowl, and rollers, there being an annular air passage between the outer wall of the bowl and the enclosing wall of the casing, means for forcing air upwardly through this annular passage to carry away in suspension pulverized material thrown from the bowl into the air stream, a substantially annular choke means mounted in the passage adjacent the upper edge of the bowl for restricting the effective width of the air passage, and means for adjusting the diameter of the choke and hence the effective width of the air passage, said choke means being yieldable to permit the effective width of the air passage to be temporarily increased at any location throughout the circumference.

6. A mill comprising a closed casing, a bowl centrally mounted within the casing for rotation about a vertical axis, means for rotating the bowl,

means for introducing material to be ground into,

the bowl, a plurality of spaced apart rollers mounted to engage inside the upwardly and outwardly extending wallof the bowl and grind the material between the bowl and rollers, there being an annular air passage between'the outer wall of the bowl and the enclosing wall of the casing, means for forcing air upwardly through this annular passage to carry away in suspension pulverized material thrown from the bowl into the air stream, a substantially annular choke means mounted in the passage adjacent the upper edge of the bowl for restricting the effective width of the air passage, said choke means comprising a plurality of independently movable sections substantially'abutting end to end, and means for supporting each section from the casing so that it may be adjusted toward or from the bowl, said supporting means being yieldable to permit the width of the'passage between the section and bowl to be temporarily increased.

7. A mill comprising a closed casing, a bowl centrally mounted Within the casing for rotation about a vertical axis, means for rotating the bowl, means for introducing material to be ground into the bowl, a plurality of spaced apart rollers mounted to engage inside the upwardly and outwardly extending wall of the bowl and grind the material between the bowl and rollers, there bepulverized material thrown from the bowl into the air stream, a substantially annular choke means mounted in the passage adjacent the upper edge of the bowl for restricting the effective width of the airpassage, said choke means comprising a plurality of independently movable sections substantially abutting end to end, each section being pivotally supported adjacent its upper edge on the casing wall, and means for adjustably holding the lower portion of the section toward the outer surface of the bowl to select the effective width of the air passage, said means comprising a spring against which the section may be pushed out to temporarily increase the width of the passage.

8. A mill comprising a closed casing, a bowl mounted within the casing for rotation about a vertical axis, means for rotating the bowl, means for introducing material to be ground into the bowl, a plurality of spaced apart rollers mounted to engage inside the upwardly and outwardly extending wall of the bowl and grind the material between the bowl and rollers, there being,

an annular air passage between the outer wall of the bowl and the enclosing wall of the casing, means for. forcing an air stream upwardly through this annular passage to carry away in suspension pulverized material thrown from the bowl, normally stationary deflecting means mounted in the upper outer portion of the casing for deflecting back into the bowl portions of the material thrown from the bowl through the air stream, means, for collecting and withdrawing bowl, a plurality of spaced apart rollers mounted 1 to engage inside the upwardly and outwardly extending wall of the bowl and grind the material between the bowl and rollers, there being ananverized material thrown from the bowl, normally stationary deflecting means mounted inthe upper outer portion of the casing for deflecting back into the bowl portions of the material thrown from the bowl through the air stream, means for collecting and withdrawing from the lower portion of C the casing heavy waste material falling down through the air passage, choke means mounted in the air passage for restricting the effective area of the passage, said means comprising a plurality of independently movable sections substantially abutting end to end to form a substantially continuous choke ring, each section being pivotally supported adjacent its upper end on the casing wall, and adjustable means for holding the lower portion of the section toward the bowl to provide an air passage of selectable width between the section and bowl, said adjustable means comprising a spring permitting the section to be pressed out to temporarily widen the passage and permit large waste material to fall therethrough.

10. A mill comprising a closed casing, a bowl mounted within the casing for rotation about a vertical axis, means for rotating the bowl, means for introducing material to be ground into the bowl, a plurality of spaced apart rollers mounted to engage inside the upwardly and outwardly extending wall of the bowl and grind the material between the bowl and rollers, there being an annular air passage between the outer wall of the bowl and the enclosing wall of the casing, means for forcing an air stream upwardly through this annular passage to carry away in suspension pulverized material thrown from the bowl, normally stationary deflecting means mounted in the upper outer portion of the casing for deflecting back into the bowl portions of the material thrown from the bowl through the air stream, means for collecting and withdrawing from the lower portion of the casing heavy waste material falling down through the air passage, choke means mounted in the air passage for restricting the effective area of the passage, said means comprising a plurality of independently movable sections substantially abutting end to end to form a substantially continuous choke ring, each section being pivotally supported adjacent its upper end on the casing wall, the normally stationary deflecting means being mounted on certain of the sections, and spring means for yieldingly holding the lower portion of the section toward the bowl to provide a restricted air passage between the bowl and section, which passage may be temporarily widened to permit the downward passage of waste material by pressing out the section against the spring means.

, WILFRED R. WOOD. 

